The present invention relates generally to printers and more particularly, to a method and system for aligning pens of a color printer based on the detected hue of overlapping test patterns.
Typically, four-color ink-jet printers have replaceable print cartridges providing cyan (C), yellow (Y), magenta (M) and black (K) ink printing. In such printers, four separate color cartridges are provided, rather than providing them in a mono-block configuration. Precise alignment among the various print cartridges, or pens, is required to produce high quality print without noticeable dot misregistration, color variegation or other undesirable visual effects. Thus, in a four-color printer wherein a black ink pen and three color ink pens are provided in the form of separate pens, alignment between the independent, and possibly slightly misaligned, pens is required. Such inter-pen or inter-color misalignment, of course, is not limited to the case where the various pens are physically separate, as misalignment may result from dimensional tolerances in the manufacture of, for example, a mono-block pen having two or more integrated print cartridges and associated ink droplet outlets or nozzles. In any event, the present invention arises from recognition of the fact that such misalignment, or misregistration, between two or more ink pens can be adjusted for by a shift of the virtual image as between the two colors prior to printing.
Previous methods for making such alignment adjustments generally have been limited to two classes of solutions. The first class of solutions requires user intervention and interaction, and typically involves printing a series of patterns on media and then requiring the user to identify which pattern is best aligned. This solution is limited in accuracy in that the user is depended upon to pick the best calibration value. The second class of solutions requires the use of an optical measurement system that monochromatically reads bars and lines printed by all of the print heads. This solution is limited in that only using one light source diminishes the ability to accurately scan all the colors. For example, if a blue illuminant is used, detection of cyan ink suffers.
There is a need for an accurate, inexpensive method of pen alignment for multi-pen color printers that does not require user input.
A pen alignment method for a multi-pen printer is provided, the method including directing a first pen to print a first pattern of a first color, directing a second pen to print a second pattern of a second color in a predetermined relative alignment with the first pattern to form a test block, determining an actual hue of the test block via spectral analysis of the test block using a color sensor, and comparing the actual hue of the test block with an expected hue of the test block to determine whether the first and second pens are misaligned relative to each other, wherein the expected hue of the test block is the hue that would be detected if the first pen and second pen were correctly aligned.